The invention relates to hydraulic gear pumps or gear motors with internally or externally meshing helical gears, in which pressure port connected and suction port connected relief grooves have been formed in a special way in the housing and/or the stationary parts, positioned in the pump facing the lateral faces of the helical gears. Known gear pumps with straight gears have the disadvantage, that the enclosed tooth cavity formed in the meshing area changes its volume very quickly, by which the nearly incompressible fluid can enter and leave the tooth cavity only with great difficulty through the relatively small relief areas in the relief grooves. The fluid in the enclosed tooth cavity s considerably compressed and decompressed in spite of possibly theoretically well-dimensioned relief grooves, which cause pressure pulsations, cavitation and noise. Concerning the normally used straight gears, this phenomenon cannot be avoided, because the size of the relief area as a function of the rotation angle of the driving gear cannot be larger than when optimally dimensioned relief grooves are used, i.e. grooves, which have been positioned in the meshing area, approximately symmetrically with respect to the plane through the two rotation axes, preferably at both lateral faces of the gears. To achieve a considerably reduced fluctuation in the rate of flow and of torque, a well-known method is to decrease the tooth clearance to zero or nearly zero. By zero should be understood a tooth clearance that is less than the normal tooth clearance of say 0.3 mm. Besides the landwidth between the pressure port connected and the suction port connected relief grooves has been reduced to half the value. Even more acutely than with a gear pump with tooth clearance the problem of trapped fluid and cavitation presents itself.